1. Field of the Invention
The present invention generally relates to an automatic lateral guidance control system for controlling the direction of a moving vehicle along a predetermined path, and more particularly, to an improved vehicle controller for use in an automatic lateral guidance control system for controlling the direction of a motor vehicle on a highway. So-called "Automated Highways" are presently being contemplated, which will include vehicular-based systems that will automatically control the motor vehicle's speed, steering and braking, in order to substitute for the driver as a prime source of control over the vehicle. The expected advantages of such systems will be to improve the overall flow of traffic and increase highway safety. The present invention is directed to such a vehicular-based system for automatically controlling vehicle direction, which accurately guides a vehicle along a path while providing a comfortable ride for passengers.
2. Description of the Prior Art
A variety of conventional guidance systems are used for controlling the movement of vehicles travelling along a predetermined path such as, for example, robotic material handling guidance systems. In some applications, a "robotic vehicle" for moving materials between separate points in a warehouse or storage area without human intervention, is provided with an automated steering control system that utilizes an inductive sensor mounted near the bottom of the vehicle in order to sense a current passing through a thin wire disposed either at or below the surface of a predetermined pathway. The inductive sensor senses the magnetic field radiated from the wire and, using conventional phase-detection techniques, produces an output signal which indicates the extent to which the vehicle has drifted laterally from the desired course. The output signals from the sensor are provided to a vehicle control circuit that typically converts the sensor's output signal into control error signals which are used to direct the vehicle back on course.
These inductive types of lateral guidance control systems have experienced some success in relatively slow-moving, industrial materials handling applications. However, these systems are considered to have serious drawbacks when they are contemplated for controlling motor vehicles moving at appreciable speeds on a highway. For example, the magnetic field radiated by a current-conducting wire disposed in the surface of the road may be distorted by metallic structures along the roadway or by stray magnetic fields from nearby power lines. Such inductive sensors are highly prone to sensing spurious signals radiated by other electromagnetic sources. In addition, such a system requires the installation and maintenance of power cables, transformers and power supplies along the road, which add an appreciable cost to such a system. Furthermore, the performance of such a system is severely limited because the inductive sensor cannot "look-ahead" as a human driver does. Inductive sensor systems can only react to the magnetic field received from the roadway immediately beneath the vehicle. Consequently, without a "look-ahead" capability, the reaction times of the inductive sensor control systems are very slow in comparison with those of a driver.
In order to overcome the above-discussed disadvantages of the inductive sensor type vehicle guidance control systems, a number of automatic guidance systems have been proposed which use optical sensors to detect reflected beams of light energy from a reflector, reflective stripe or other light reflective medium disposed at the side of the road or applied to the road's surface. The vehicle's position and direction is then determined with respect to the reflector. An example of such a "look-ahead" technique is illustrated in U.S. Pat. No. 4,049,961 to Marcy. Marcy discloses an automatic guidance system for a motor vehicle which includes an optical laser transmitter/ receiver assembly. A series of spaced-apart responders (i.e., light reflective devices) are disposed in a single row parallel to the centerline of the roadway, or in a pair of rows on opposite sides of the centerline, for reflecting radiant energy from the laser transmitter back to the receiver. As shown in Marcy, the laser transmitter radiates two overlapping beams which are amplitude-modulated by sine waves that are 180 degrees out of phase. The receiver merges the two reflected beams into a single beam that is subject to a cyclic translatory shift in amplitude. The amplitude shift is translated into a voltage whose amplitude varies in accordance with the position of the vehicle. In other words, a comparison of the phase differences between the transmitted and reflected beams provides a determination of the vehicle's location with respect to the reflectors. However, the use of such a system typically requires the use of a high powered laser transmitter, which can have a prohibitively high cost. More significantly, however, the conventional laser-controlled, automatic guidance systems have limited tracking performance or accuracy with respect to controlling the vehicle's direction, because such systems do not take into account the vehicle's speed. For example, the reaction time needed to steer the vehicle in response to sensed changes in the direction of the road increases as the vehicle's speed increases. Thus, although the conventional automatic guidance systems for motor vehicles may be considered "look-ahead" systems, the reaction time for the conventional systems is still limited at the higher vehicle speeds. Nevertheless, the present invention provides a novel arrangement for a "look-ahead" automatic lateral guidance control system that accounts for the speed of the vehicle and thereby increases the tracking performance and accuracy of the system, while providing a comfortable travelling environment.